Method for manufacturing a microlens substrate and method for manufacturing a liquid crystal panel

ABSTRACT

Disclosed herein is a method for manufacturing a microlens substrate which is excellent in chemical resistance and light fastness to intense light irradiation, and is capable of forming a microlens substrate of a high accuracy of form. The method includes the steps of: forming a lens-shaped curve at a surface side of a transparent substrate; forming an inorganic material film on the transparent substrate so as to bury the curve therewith; and planarizing the surface of the inorganic material film to provide a microlens where the curve is buried with the inorganic material film.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method for manufacturing a microlenssubstrate wherein a plurality of microlenses are formed and arranged,and also to a method for manufacturing a liquid crystal panel using themicrolens substrate.

[0002] In recent years, flat displays have shown a pronounced spread andbreakthrough on the market, including plasma displays, liquid crystaldirect view, large-sized screen displays, field emission displays, andorganic and inorganic EL displays. These have gained a public favor asbeing flat and large in size and having a thin design called “Wall-hungTV”, which is considered as one of factors of making a breakthrough.

[0003] On the other hand, extensive developments have been made onprojectors using light bulbs such as LCD (liquid crystal display), DMD(digital mirror display), LCOS (liquid crystal on silicon) and the like.Although these cannot be made so thin as “wall-hung type” as set outhereinabove, rear projection TV is fully responsible for high imagequality and low costs and has the ability of playing a role oflarge-sized displays. Moreover, with projectors, they have suchapplicability as to be arbitrarily selectable in projection frame sizethat is an intrinsic characteristic property thereof, like front AVprojectors. In addition, they have the feature in that their portabilityis good as a result of the advance in miniaturization, thus ensuringoutdoor use. It is thus believed that in some future day, these displayswould begin to be put on the respective fields of market depending onthe characteristic feature thereof.

[0004] In a high-definition liquid crystal panel (liquid crystal lightbulb) for conventional liquid crystal projectors, a microlens substratewherein a microlens is provided in every pixel is used. For theformation of the microlens substrate, a silica substrate or differenttypes of glass substrates are employed, and application of (a) wetetching technique, (b) 2P (photo-polymerization) technique and (c) dryetching technique has been reduced into practice.

[0005] Among these techniques, the wet etching technique (a) isillustrated with reference to FIGS. 7A to 7E. Initially, as shown inFIG. 7A, a resist pattern 102 is formed on a substrate 101 made of glassor silica. Next, as shown in FIG. 7B, a lens-shaped concave curve 101 ais formed in the substrate 101 by isotropic etching through the mask ofthe resist pattern 102 with use of a HF etchant. After removal of theresist pattern 102, a resin 103 is applied onto the substrate 101 tofill the inside of the concave curve 101 a with the resin as shown inFIG. 7C. Next, as shown in FIG. 7D, a cover glass 104 is attachedthrough the resin 103 on the substrate 101, thereby forming a microlens105 wherein the resin 103 is filled within the concave curve 101 a.Thereafter, as shown in FIG. 7E, an ITO electrode 106 is formed on thecover glass 104 to complete a microlens substrate 107. It will be notedthat for the isotopic etching mask used in FIG. 7B, a material such as ametal (chromium or the like) or an impurity-containing polysilicon,which is resistant to a HF etchant, may be used.

[0006] Alternatively, another method may be used wherein a resistpattern on a substrate is thermally processed into a lens form, and thesubstrate is etched through a mask of the pattern to transfer alens-shaped convex curve in the substrate (see Japanese Laid-open PatentLaid-open No. 2001-92365, particularly at [0008] to [0009] and FIG. 6).

[0007] In both methods illustrated hereinabove, the microlens is formedof a resin, and the source of lens power is based on the difference inrefractive index between the resin and the substrate. Especially, in the2P technique (b), the use of a UV-curable resin is essential therefor,and it is unavoidable to use a UV-curable resin.

[0008] The resins used for such a microlens substrate should have thefollowing properties (1) to (6).

[0009] (1) High transmittance in a visible light region.

[0010] (2) High heat resistance (to a temperature of about 200° C.)standing use in the manufacturing process of a liquid crystal displayafter the formation of microlenses.

[0011] (3) Goods light fastness.

[0012] (4) Good chemical resistance, or a resistance to chemicals(alcohols, ketones, and waterproofing) in subsequent processes.

[0013] (5) High reliability such as of not causing cloudiness by theinfluence of high temperatures, high humidity, low temperatures and heatcycles and undergoing little change of refractive index withoutcracking. Optimum viscosity (of about 100 cps to500 cps), good adhesionand adhesion strength for ensuring uniformity in thickness of a resinfilm.

[0014] However, only a very small number of resins which actually meetthe properties (1) to (6) in practice are known. Hence, it is the usualpractice to search for a resin that meets such requirements as set outabove and optimally design the shape of microlens according to therefractive index depending on the type of device, with the attendantproblem that the selection of material is difficult. Especially, where aresin for microlens is used as an adhesive or an adhesive resin used isof a type different from that of a microlens, the requirements otherthan the visible light transmittance (1) pose problems to all ofactually existing liquid crystal displays.

[0015] For instance, the problem involved in improving light fastness(3) is as follows. The improvement in brightness of recent liquidcrystal projectors increasingly places importance on the improvement inlight fastness of a resin (i.e. an organic material) for arranging aliquid crystal panel. Especially, if light in a blue region (in thevicinity of 400 nm), which is an emission region of a lamp used for theprojector, is absorbed only slightly, the resin is liable to be degradedto a non-negligible extent owing to the improvement of brightness. Inordinary projectors, light in a wavelength region of 420 nm or below iscut off by means of a UV-IR cut filter or the like. However, it has nowbeen experienced that a slight variation in performance of UV-IR cutfilters permits such a non-negligible degree of resin degradation as tooccur by the action of light of the component contained within theabove-mentioned wavelength region. In the worst case, the resin willundergo yellowing or browning along with an instance where the resinbecomes wavy such as by a deformation stress caused during the use of aprojector.

[0016] With respect to the chemical resistance (4), alcohols and ketonesare used in a LCD assembling process including cleaning steps ofsubstrate and panel. Only slight dissolution in these solventsinfluences a voltage retention of LCD and contributes to ion conduction,thus bringing about the degradation of LCD. Moreover, if such a resin isformed on an aligned film even in the form of a monomolecular layer, avariation in pretilt angle of liquid crystal molecules, an anchoringcharacteristic of liquid crystals molecules and working operation areinfluenced.

[0017] Further, with respect to reliability (5), resins are usually notresistant to moisture. Water molecules fundamentally degrade adhesion bydiffusion in resin, and the refractive index (n=1.33) of water isgenerally smaller than refractive indices of resins, so that as amoistureproof test times passes, the resin refractive index changes,thereby causing the power of microlens to be degraded and the focaldistance to be changed.

[0018] The requirement (6) presents problem particularly on thedifference in thermal expansion between a substrate material and aresin. In general, the difference in thermal expansion is on the orderof magnitude of double-digit or over.

[0019] In general, organic matters are low in refractive index, forwhich it is necessary to form a lens deeply for the purpose of achievinghigh brightness. Usually, it is more difficult to make a deep lens. Whenusing etching or the like, uniformity and productivity are adverselyinfluenced, and where a substrate size is increased for cost cutting, adifficulty is involved in the uniformisation of a lens shape.

SUMMARY OF THE INVENTION

[0020] It is therefore an object of the invention to provide a methodfor manufacturing a microlens substrate which is excellent in chemicalresistance and light fastness to intense light irradiation and iscapable of forming microlenses of high shape precision.

[0021] It is another object of the invention to provide a method formanufacturing a liquid crystal panel using the microlens substrate.

[0022] In order to achieve the above objects of the invention, there isprovided, according to the invention, a method for manufacturing amicrolens substrate, which includes the steps of forming a lens-shapedcurve in a surface side of a transparent substrate, forming an inorganicmaterial film on the transparent substrate so as to bury the curvetherewith, and planarizing the surface of the inorganic material to burythe curve with the inorganic material film.

[0023] The method for manufacturing a liquid crystal panel according tothe invention is characterized by including, after the formation of themicrolens as set out above, forming a thin. film transistor at aposition corresponding to a peripheral portion of the microlens on theinorganic material film to provide a microlens substrate, providing acounter substrate in face-to-ace relation with the microlens substrateat the side where the thin film transistor has been formed, and sealedlyplacing a liquid crystal layer between these substrates.

[0024] According to these methods of manufacturing a microlens substrateand a liquid crystal panel, the microlens is formed by burying alens-shaped curve formed in the transparent substrate with an inorganicmaterial film, so that the microlens substrate can be constituted onlyby use of an inorganic material without use of a resin. Thus, amicrolens substrate having good chemical resistance and light fastnesscan be obtained. In addition, the heat resistance is so improved that itbecomes possible to perform steps having a thermal treatment, such asthe step of forming a thin film transistor on a flattened or planarizedinorganic material film. In this way, one is enabled to form a thin filmtransistor while registering against a microlens in high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIGS. 1A to 1G are, respectively, a sectional view illustrating afirst example of a method of manufacturing a microlens substrateaccording to a first embodiment of the invention;

[0026]FIGS. 2A and 2B are, respectively, a sectional view illustrating asecond example of a method of manufacturing a microlens substrateaccording to a second embodiment of the invention;

[0027]FIGS. 3A to 3D are, respectively, a sectional view illustrating athird example of a method of manufacturing a microlens substrateaccording to a third embodiment of the invention;

[0028]FIG. 4 is a sectional view showing an arrangement of a liquidcrystal panel according to a fourth embodiment of the invention;

[0029]FIG. 5 is a sectional view showing a modification according to thethird embodiment;

[0030]FIG. 6 is an illustrative view showing an essential part o aliquid crystal projector using the liquid crystal panel of the thirdembodiment; and

[0031]FIGS. 7A to 7E are, respectively, a sectional view illustratingthe steps of a method for manufacturing a known microlens substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The embodiments of the invention are described in detail withreference to the accompanying drawings. It will be noted that a methodfor manufacturing a microlens substrate for a liquid crystal panel witha 0.7 inch×GA (extended graphics array: 1024×768 pixels) display and amethod for manufacturing a liquid crystal panel are described in thisorder.

[0033] <Embodiment 1>

[0034]FIGS. 1A to 1B are, respectively, a sectional view illustrating afirst example of a method of manufacturing a microlens substrateaccording to the invention. The first embodiment is illustrated withreference to these figures.

[0035] Initially, as shown in FIG. 1A, a resist film 3 is formed on atransparent substrate 1, which has, for example, a diameter of 6 inchesand is made of fused silica (or Neoceram). In this case, the resist film3 is formed in a thickness of 10 μm according to a spin coatingtechnique.

[0036] Next, as shown in FIG. 1B, the resist film 3 is subjected tolithographic treatment at the surface side to form an array oflens-shaped concave curves which are a basic pattern of microlenses. Inthis embodiment, concave curves 3 a are formed in the respective pixelregions of about 14 μm×14 μm created by partitioning a display region atthe center of the surface side of the transparent substrate 1.

[0037] In this lithographic treatment, multiple exposure is carried outwherein a plurality of exposure masks (multiple mask) 3 is used to carryout pattern exposure to the resist film 3 successively. It is to benoted that exposure using an i-ray stepper is performed in this multipleexposure. After the multiple exposure, the resist film 3 is developedwith use of a coater developer.

[0038] In the multiple exposure, there is used a multiple mask thatpermits, for example, an aspheric lens-shaped concave curve 3 a to beformed. This lens shape is appropriately set depending on the differenceof refractive index between the materials used for constituting themicrolens. For instance, where a microlens formed in the following wayis constituted of fused silica (refractive index n=1.46) used to form alens-shaped concave curve and Al₂O₃ (refractive index n 1.58 to 1.65)filled in the concave curve, a lens shape is so set as to have anaspheric constant k=about −0.95 to −0.8 and a focal distant f 40 to 45μm (in air). In this condition, the lens depth is at approximately 5 to7 μm. The number of masks in the multiple mask is at about ten.

[0039] It will be noted that after the lithographic treatment, thestepped shape of the concave curve 3 a may be smoothened through thermaltreatment.

[0040] Next, as shown in FIG. 1C, the lens-shaped concave curves 3 aformed at the surface side of the resist film are transferred from theresist film 3 to the transparent substrate 1 by dry etching. In thismanner, the lens-shaped concave curves 1 a are formed in the surface ofthe transparent substrate 1. This concave curve 1 a has a lens depthd=approximately 5 to 7 μm. In this embodiment, a parallel plate RIEsystem is used, for example, wherein etching is carried out such thatthe pressure within an etching atmosphere is kept at 0.1 Pa or over andthe electrode power is kept at 0.2 kW or over, and CF₄, CF₃H or CF₂H₂ isused as an etching gas. It will be noted that a gas such as SF₆, C₃F₈ orthe like may also be used for the etching gas. In this etching, theetching selection ratio may be set within a range of resist film 3:substrate 1=about 1:1 to 7:1.

[0041] The steps set forth hereinabove may be effected according to themultiple exposure method described, for example, in Japanese PatentLaid-open Nos. Hei 7-191209, Hei 8-219808 and the like. The patternexposure using the above-stated lithography may be carried out by a graymask technique in place of the multiple exposure method.

[0042] Thereafter, as shown in FIG. 1D, an inorganic material film 5 isformed on the transparent substrate 1, formed with the concave curves 1a thereon, in a thickness sufficient to bury the concave curve 1 atherewith. The inorganic material film 5 is formed, for example, byusing at least one of Al₂O₃ (refractive index n=1.62 to 1.70), HfO₂(refractive index n=1.95 to 2.03), Ta₂O₅ (refractive index n=2.03 to2.12), Nb₂O₅ (refractive index n=2.23 to 2.32) and ZrO₂ (refractiveindex n=1.98 to 2.05).

[0043] The inorganic material film 5 is formed by a vacuum depositionmethod wherein an electron beam is irradiated on an inorganic materialto apply particles of the material on the transparent substrate 1thereby building up and forming a film. It will be noted that for theformation of the inorganic material film 5 made of Al₂O₃, oxygen may beadded to an atmospheric gas so as to keep the stoichiometry of Al₂O₃.The inorganic material film 5 may be formed by a sputtering method, aCVD method, or a MOCVD (metallo-organic chemical vapor deposition)method using TMA (trimethyl aluminium) or the like.

[0044] With the case of the lens depth (i.e. a depth of the concavecurve 1 a) d=approximately 5 to 7 μm as set out hereinabove, theinorganic material film 5 is formed in a thickness of about 15 μm sothat the concave curve 1 a is fully buried with the inorganic materialfilm 5.

[0045] The inorganic material film 5 may be formed by mixing suchmaterials as mentioned above at appropriate ratios for the purpose ofcontrolling a refractive index as desired. If the vacuum depositionmethod described above is used, an electron beam is irradiated on aplurality of materials, respectively, thereby depositing the pluralityof materials on the transparent substrate 1 simultaneously. Forinstance, where it is intended to from an inorganic material film 5having a refractive index n=about 1.80, Al₂O₃ and HfO₂ are placed indifferent crucibles within a vacuum deposition chamber and are,respectively, irradiated with an electron beam, thereby causing Al₂O₃and HfO₂ to be deposited on the surface of the transparent substrate 1simultaneously. When the applied power of the electron beam irradiatedon the respective materials is appropriately controlled, the amounts ofthe deposited materials can be controlled, with a refractive index beingoptimized.

[0046] Subsequently, as shown in FIG. 1E, the inorganic material film 5is planarized to form a microlens 7 wherein the inorganic material film5 is buried in the concave curved 1 a of the substrate 1. For example,abrasion is executed to planarize the inorganic material film 5, in thiscase. Where the inorganic material film is formed of Al₂O₃, cerium oxide(CeO₂) is used as an abrasive. In this way, the inorganic material film5 is planarized on the surface thereof, and the inorganic material film5 is polished to such an extent that the film thickness on theplanarized portion of the transparent substrate 1 is at about 3 to 5 μm.It will be noted that after completion of the polishing, the polishedsurface should be cleaned.

[0047] Next, as shown in FIG. 1, a cover film 9 is formed on theplanarized inorganic material film 5. The cover film 9 should preferablybe formed of a material which has substantially the same coefficient ofthermal expansion as the transparent substrate 1. It will be noted thatthe thickness of the cover film 9 is so arbitrarily set as to benecessary for performance on combination with the thickness of theinorganic insulating film 5.

[0048] In this embodiment, the cover film 9 made of SiO₂ is formed in athickness of about 19 μm by a sputtering method, for example. Thesputtering conditions in this case includes an inner pressure in afilm-forming atmosphere of 0.1 to 0.6 Pa, a substrate temperature of100° C. to 350° C. and a sputtering gas of Ar and O₂. It will be notedthat the formation of the inorganic material film 5 made of SiO₂ may becarried out by a CVD method or a vacuum deposition method. In addition,a SiN film is thinly formed by a plasma CVD method as the cover film 9so that the stress involved therein is more positively controlled. Moreparticularly, the formation of a SiN film by a plasma CVD method allowsa wider range of control of film stress by a two frequency method thanin the case of a SiO₂ film.

[0049] Next, as shown in FIG. 1G, a transparent electrode film 11 isformed on the cover film 9. In this embodiment, a transparent electrodefilm 11 made of ITO (indium tin oxide) is formed in a thickness of about140 nm by a sputtering method. In this manner, the total opticalthickness t of the inorganic material film 5, cover film 9 andtransparent electrode film 11 formed on the planarized portion of thetransparent substrate 1 is such that t=about 18 μm (a value calculatedin air).

[0050] According to the procedure set forth hereinabove, a microlenssubstrate 13 is obtained wherein a plurality of microlenses 7 are formedin array on the surface of the transparent substrate 1.

[0051] Where a liquid crystal panel using the thus obtained microlenssubstrate 13 is formed, an alignment film is formed on the transparentelectrode film 11. On the other hand, there are provided a pixelelectrode and an ordinary TFT substrate wherein the surface sideprovided with a thin film transistor (hereinafter referred to simply asTFT) for driving the pixel electrode is covered with an alignment film.The alignment film-formed faces of the microlens substrate 13 and theTFT substrate are placed in face-to-face relation with each other,between which a crystal liquid layer is filled and sealed therebyforming a liquid crystal panel.

[0052] According to the manufacturing method of the first embodimentillustrated hereinabove, the concave curves 1 a formed in thetransparent substrate 1 made of fused silica, glass or the like are,respectively, buried with the inorganic material film 5 to formmicrolenses 7. Thus, a microlens substrate 13 constituted of aninorganic material alone can be obtained without use of a resin. Thispermits a microlens substrate 13 having excellent chemical resistanceand light fastness to be obtained without causing many troubles ascribedto the use of resin. In the liquid crystal panel using such a microlenssubstrate 13, because any resin is used for the microlens substrate 13,cross contamination with a resin during a processing procedure can beprevented. In the liquid crystal panel using such a microlens substrate,the liquid crystal layer is prevented from pollution with a resin. Thus,the influence of a resin on the liquid crystal layer can be perfectlyexcluded, making it possible to obtain a liquid crystal panel havinggood display characteristics.

[0053] Further, since any resin is not used, discrepancies ascribed tothe difference in coefficient of thermal expansion between the resin anda substrate can be avoided. Additionally, when using a resin, a lensdepth has been set largely in view of the difference in refractive indexfrom the transparent substrate. The use of an inorganic material filmthat allows selection of a material having a large refractive indexenables one to make a small lens depth, facilitating easy formation of alens-shaped curve. This leads to improved uniformity of a pluralitycurves. From the foregoing, it becomes possible to design a large-sizedmicrolens substrate 13.

[0054] As having stated hereinbefore, the light fastness of themicrolens substrate 13 can be improved. When a liquid crystal panelusing the microlens substrate 13 is set in a liquid crystal projectorfor use as a light bulb so as to increase the quantity of light from alamp of the liquid crystal projector, thus enabling one to achievehigher brightness. This results in a lower gain of a screen, with thepossibility that a wide viewing angle can be improved.

[0055] <Embodiment 2>

[0056] A second example of a method for manufacturing a microlenssubstrate according to the invention is illustrated with reference toFIGS. 2A and 2B which are, respectively, a sectional process view.

[0057] Initially, as shown in FIG. 2A, a resist pattern 21 is formed ona transparent substrate 1 similar to that used in the first embodimentby a lithographic technique. This resist pattern 21 has a hole 21 a atthe center of a lens-shaped concave curve to be formed, which is a basicpattern of a microlens.

[0058] Next, as shown in FIG. 2B, the transparent substrate 1 isisotropically etched through a mask of the resist pattern 21. Thisallows the isotropic etching to proceed around the hole 21 a of theresist pattern 21, and concave curves 1 a are formed in array within therespective pixel regions of a size of about 14 μm×14 μm formed bypartitioning a display region at the center of the surface side of thetransparent substrate 1. The respective concave curves 1 a formed inthis way are spherical in shape. After completion of the etching, theresist pattern 21 is removed.

[0059] It will be noted that he mask (mask pattern) used for theisotropic etching for the transparent substrate 1 should not beconstrued as limiting to the resist pattern 21. This mask pattern may beone which is made of a metal film obtained by pattern etching through amask of the resist pattern or is made of a material such asimpurity-containing polysilicon. More particularly, the pattern is notcritical so far as it is resistant to an etchant used for the isotropicetching.

[0060] After the steps stated hereinabove, a microlens substrate 13 canbe obtained by carrying out the procedures as illustrated in the firstembodiment with reference to FIGS. 1A to 1G. Using this microlenssubstrate 13, a liquid crystal panel can be formed in the same manner asillustrated in the first embodiment.

[0061] In the manufacturing method of the second embodiment illustratedhereinabove, the microlens 7 is formed by burying the lens-shapedconcave curve 1 a formed in the transparent substrate 1 made of fusedsilica, glass or the like with the inorganic material film 5, so thatsimilar effects as in the first embodiment can be obtained.

[0062] <Embodiment 3>

[0063] Next, a method for manufacturing a microlens substrate accordingto a third embodiment of the invention is illustrated with reference toFIGS. 3A to 3D which are, respectively, a sectional process view. Itwill be noted that these sectional process views corresponding toenlarged views of an essential part of FIGS. 1A to 1G and 2A to 2B.

[0064] Initially, the steps illustrated with reference to FIGS. 1A to 1Fin the first embodiment are, for example, carried out to form amicrolens 7 wherein a concave curve 1 a of a transparent substrate 1 isburied with an inorganic material film 5 as shown in FIG. 3A, andfurther to form a cover film 9. It will be noted that the procedure upto and including this step may be carried out by application of theprocedure of the second embodiment.

[0065] Next, as shown in FIG. 3B, a light-shielding film pattern 31 isformed on the cover film 9. This light-shielding film pattern 31 isdisposed at a position surrounding individual microlenses 7 or along theperipheral edge of the respective pixels, thus being placed incoincidence with the wiring positions of a gate wiring of TFT and asignal wiring which are described hereinafter. Such a light-shieldingfilm pattern 31 is formed of a layer of WSi or a transition metal suchas Ti, W, Ta, Cr or the like by a sputtering method, followed bypatterning. Alternatively, the pattern may be formed by applying themethod described in Japanese Patent No. 3 231 757 and patterning a layermade of polycide. It is to be noted that the thickness of thelight-shielding film pattern 31 is, for example, at about 200 nm.

[0066] Next, a layer insulating film 32 is formed on the cover film 9 sothat the light-shielding film pattern 31 is in a buried stated. To thisend, the layer insulating film 32 made of SiO₂ is formed in a thicknessof about 600 nm, for example, by an AP (atmospheric pressure)-CVDmethod. It will be noted that for a subsequent TFT process, this layerinsulating film 32 may be planarized by a CMP method after the formationof the layer insulating film 32.

[0067] Next, as shown in FIG. 3C, a TFT circuit 33 is formed on thelayer insulating film 32. In this case, a semiconductive thin film 34made of polysilicon is first formed on the layer insulating film 32 in athickness of about 75 nm, for example, by an LP (low pressure)-CVDmethod. Next, Si ions are implanted into the semiconductive thin film 34at about 2E15 cm⁻² according to an ion implantation method to render thefilm amorphous, followed by thermal treatment at 600° C. for about 24hours to permit solid phase growth.

[0068] It will be noted that for the formation of the polycrystallinesemiconductive thin film 34, ordinary techniques such as a hightemperature polysilicon process wherein a substrate temperature reachesabout 1000° C., a low temperature polysilicon process using an exciterlaser annealing procedure (substrate temperature: 450° C. to 600° C.) .With respect to the low temperature polysilicon process, the processreported by Katzuhide Yoshinaga et al., in “AO. 9” XGA Low TemperaturePOLY-Si TFT LCLV with stacked Storage Capacitor, SID 02 Digest, p.1013-1015 can be applied.

[0069] Next, the thus polycrystallized semiconductive thin film 34 issubjected to patterning, followed by oxidization within an oxidizingfurnace at about 1000° C. to grow an about 750 nm thick oxide film 35 asa surface layer of the semiconductive thin film 34.

[0070] Next, B⁺ ions are introduced into a TFT portion of thesemiconductive thin film 34 and As⁺ ions are introduced into a capacitorportion, both according to an ion implantation method. Thereafter, a 300nm to 400 nm thick gate electrode 36 and an upper electrode 37 of thecapacitor are, respectively, formed over the semiconductive thin film 34through the oxide film 35. The gate electrode 36 and the upper electrode37 are, respectively, formed according to a method described, forexample, in Japanese Patent No. 2993665. Thereafter, an impurity isintroduced according to an ion implantation method using the gateelectrode 36 as a mask so as to from source drain regions of the TFT.

[0071] Next, a layer insulating film 38 made of PSG (with a Pconcentration of about 2 to 4 wt %) is formed, in a thickness of about600 nm, over the layer insulating film 32 so as to cover the gateelectrode 36 and the upper electrode 37. Subsequently, a connection holearriving at the semiconductive thin film 34 is formed in the layerinsulating film 38, and a signal wire 39 and a lead wire 40 forconnection with the semiconductive thin film 34 via this connection holeare, respectively, formed. The signal wire 39 and the lead wire 40 areformed by patterning a 400 to 600 nm thick Al—Si (Si content of 0.9%)film. In this way, the TFT circuit 33 wherein TFT and the capacitor havebeen wired is formed in. the display region at the center of the surfaceside of the transparent substrate 1. This TFT circuit 33 is so arrangedas to be at a position surrounding a plurality of pixel regions dividingthe display region.

[0072] It will be noted that the formation of the TFT circuit 33 is notlimited to the above-stated procedure, and procedures set forth inJapanese Patent Nos. 3231757 and 2993665, Japanese Patent Laid-open Nos.2000-142089 and 2001-330856, and the like may be applied.

[0073] Simultaneously with the step of forming the TFT circuit 33, adrive circuit provided with a p-channel TFT may be formed at aperipheral region surrounding the display region at the surface side ofthe transparent substrate 1, thereby providing a CMOS arrangement. Inaddition, the TFT may be formed as having a LDD structure or a doublegate structure.

[0074] After the formation of the TFT circuit 33 in a manner asdescribed hereinabove, a layer insulating film 41 made of SiO₂ is formedon the layer insulating film 38 by an AP-CVD method in a thickness ofabout 400 nm so as to cover the signal wire 39 and the lead wire 40, asshown in FIG. 3D. Thereafter, a connection hole is formed in the layerinsulating film 41 so as to arrive at the lead wire 40, and a wiringpattern 42 and a light-shielding film pattern 43 that are connected tothe lead wire 40 via the connection hole are, respectively, formed.These wiring pattern 42 and light-shielding film pattern 43 are formedby subjecting a light-shielding film of a metal, such as To, W, Ta orthe like, to pattern etching.

[0075] Furthermore, an upper insulating film 44 is formed over the layerinsulating film 41 so as to cover the wiring pattern 42 and thelight-shielding film pattern 43. Thereafter, a connection hole arrivingat the wiring pattern 42 is formed in the upper insulating film 44, apixel electrode 45 connected to the wiring pattern 42 via the connectionhole is formed. This pixel electrode 45 is formed by subjecting atransparent electrode material film such as, for example, ITO or thelike to pattern etching.

[0076] In this way, a microlens substrate 50 having the TFT circuit 33for driving the pixel electrode 45 is obtained. This microlens substrate50 serves also as a TFT substrate.

[0077] Where a liquid crystal panel is formed using the microlenssubstrate 50 having such an arrangement as described hereinabove , analignment film is formed so as to cover the pixel electrode 45 therewithalthough not shown herein.

[0078] On the other hand, the microlens substrate 13 is made accordingto the procedure illustrated in the first embodiment with reference toFIG. 1 or the procedure illustrate in the second embodiment withreference to FIGS. 1 and 2, an alignment film (not shown) may be formedon the transparent electrode film 11 of the microlens substrate 13. Itwill be noted that this microlens substrate 13 may be a conventional oneusing a resin.

[0079] Next, as shown in FIG. 4, the microlens substrate 50 and themicrolens substrate 13 are so arranged that the alignment film-formedsurface (pixel electrode 45-formed surface) of the substrate 50 and thealignment film-formed surface (transparent electrode 11-formed surface)are in face-to-face relation with each other. In the respective pixelregions, the microlens substrates 13, 50 are facing each other such thata distance L between principal points P1 and P2 of the microlenssubstrates 13, 50 is substantially in coincidence with a focal distanceof the microlens 7 at the microlens substrate 50 side serving also asthe TFT substrate.

[0080] A liquid crystal layer 51 is sealedly filled between themicrolens substrate 13, 50 arranged in such a way as set forth above.

[0081] Accordingly the manufacturing method of the third embodimentillustrated with reference to FIGS. 3A to 3D, the microlens 7 can beimproved in resistance by forming the microlens 7 in a manner asillustrated in the first embodiment. This enables one to obtain themicrolens substrate 50 serving also as the TFT substrate, without thestep of bonding the microlens substrate to the TFT substrate, whereinthe TFT circuit 33 undergoing a thermal treating step is formed on theinorganic material film 5 constituting the microlens 7 and which has theTFT circuit for driving the pixel electrode 45.

[0082] More particularly, it becomes possible to form the microlens 7,followed by continuous formation of the TFT circuit 33 and the pixelelectrode 45, all on the same substrate, so that while registering withthe previously formed microlens 7, the TFT circuit 33 can be formed. Theregistration is carried out in high precision by using a stepper or amirror projector, and thus the resulting microlens substrate 50 isimproved in precision of registration between the microlens 7 and theTFT circuit 33 and pixel electrode 45 and also acts as a TFT substrateof high quality.

[0083] Since the microlens substrate 50 is obtained without bonding thetwo substrates together, the number of transparent substrates can bereduced, thus leading to the saving of substrate costs.

[0084] The liquid crystal panel 52 using the microlens substrate 50illustrated with reference to FIG. 4 has the two microlenses 7 arrangedin such a state as stated hereinbefore and sandwiching the liquidcrystal layer 51 in individual pixel regions, so that a field functionis provided and an angle of divergence of an incident ray into theliquid crystal panel.

[0085] Moreover, as stated hereinabove, the microlens 7 at the side ofthe microlens substrate 50 serving as a TFT substrate is disposed inhigh precision relative to the TFT circuit 33 and the pixel electrode45, the field function can be very efficiently developed. The variationin quantity of an output ray that depends on the degree of registrationwith the microlens can be suppressed, with an improved yield.

[0086] Further, in the manufacturing method illustrated with referenceto FIGS. 3A to 3D, such an arrangement has been described wherein afterthe formation of the cover film 9, one layer of the light-shielding filmpattern 31 is formed thereon. In this connection, however, according tothe invention, the inorganic insulation film 5 is formed such that thelens-shaped concave curve 1 a is buried with its surface beingplanarized thereby obtaining the microlens 7. In this condition, itbecomes possible to form the light-shielding film pattern directly onthe planarized inorganic insulating film 5. Accordingly, as shown inFIG. 5, two layers 31, 31 a of the light-shielding film pattern may beprovided as sandwiching the cover film therebetween.

[0087] Where such two light-shielding film patterns 31, 31 a are formed,the inorganic material film 5 is planarized, after which the first-layerlight-shielding film pattern 31 a is formed and the cover film 9 isformed so as to cover the pattern therewith. After planarization of thecover film 9 on the surface thereof, if necessary, the light-shieldingfilm pattern 31 (second layer) is formed in a manner as illustrated inthe above-stated third embodiment, followed by subsequent steps. It willbe noted that the first-layer light-shielding film pattern 31 a isformed in the same manner as with the above-stated light-shielding filmpattern 31.

[0088] In this way, the two layers of the light-shielding film patterns31, 31 a can be provided, so that the incidence of light to the TFTcircuit 33 from the back side of the transparent substrate 1 can beefficiently prevented, and the generation of an optical leakage currentcan be prevented along with disadvantages involved in image quality,such as flickers, a lowering of contrast and the like, being avoided. Inaddition, heat generation in the liquid crystal panel arranged by use ofthe microlens substrate 50 a can be released from the two layers of thelight-shielding film patterns 51, 51 a, and thus the working temperatureof the liquid crystal panel can be further reduced, thereby permittingreliability to be improved. Moreover, because light is shielded by meansof both layers of the light-shielding film patterns 31, 31 a, the marginfor the film thickness with which the degree of light-shielding in therespective layers is determined is enlarged, with the effect ofenlarging the light-shielding process margin.

[0089] Especially, in a liquid crystal projector using the liquidcrystal panel constituted by use of the microlens substrate 50 a, thedirection of emission of display light is at the side of the transparentsubstrate 1 of the microlens substrate 50 a (see, for example, DouglasHansen et al., “The-Display Applications and Physics f the Proflux (™)Wire Grid Polarizer”, SID Digest 2002, p. 730 to p. 733). It will benoted that the liquid crystal panel using the microlens substrate 50 ahas such an arrangement wherein the microlens substrate 50 of the liquidcrystal panel 52 illustrated with reference to FIG. 4 is replaced, in asimilar arrangement, by the microlens substrate 50 a.

[0090] More particularly, as shown in FIG. 6, in the liquid crystalprojector, the liquid crystal panel 52 a, in which the liquid crystallayer 51 is sandwiched between the microlens substrate 50 a and themicrolens substrate 13 disposed in face-to-face relation with the formerone, is placed between two polarizing plates 54, 55. Of lamp rays hincident from a polarizing plate 54 of the facing side microlenssubstrate 13, light h1 emitted after passage through the polarizingplate 54, the liquid crystal panel 52 a and a polarizing plate 55 servesas a display light ray. However, in case where the polarizing plate 55at the emission side is made of an inorganic polarizing plate and ablack display is effected, light h2 is reflected at the polarizing plate55 toward the liquid crystal panel 52 a side and enters the liquidcrystal panel 52 a as returned light h1′. To prevent the returned lighth1′ from the transparent substrate (1) side of the microlens substrate50 a from entering the TFT circuit 33 is very important for preventingthe generation of an optical leakage current and the disadvantages inimage quality such as flickers, a lowering of contrast and the like.

[0091] Accordingly, as illustrated with reference to FIG. 5, using themicrolens substrate 50 serving also as the TFT substrate wherein thelight-shielding film patterns 31, 31 a having a double-layeredstructure, such returned light h1′ can be reliably prevented fromentering the TFT circuit 33, thus enabling one to improve the imagequality of the liquid crystal projector.

[0092] It will be noted that in the microlens substrate serving also asa TFT circuit, such an arrangement may be provided wherein thefirst-layer light-shielding pattern 31 a shown in FIG. 5 alone is formedand the second-layer light-shielding film pattern 31 is not formed.

[0093] In the respective microlens substrates serving as the TFTsubstrates described above, where a semiconductive thin film for the TFTcircuit is formed according to a low temperature process, it is possibleto use the microlens substrate as a light diffusion layer of a directview panel.

[0094] In the first to third embodiments stated hereinbefore, anarrangement wherein the transparent electrode film 11 and the TFTcircuit 33 are formed on the cover film has been illustrated. However,the inorganic material film 5 left on a planarized portion of thetransparent substrate 1 obtained after the planarization is set as thickwithout formation of the cover film 9. The transparent electrode film 11may be formed directly on the planarized inorganic insulating film 5. Inthis case, the step of forming the cover film 9 is omitted, thus leadingto improved productivity.

[0095] As stated hereinbefore, according to a method for manufacturing amicrolens substrate of the invention, a lens-shaped curve formed in atransparent substrate is planarized by burying with an inorganicmaterial film, thereby forming a microlens. Thus, it becomes possible toobtain a microlens substrate which is excellent in chemical resistanceand light fastness and this provided with microlenses of a high accuracyof form. Moreover, according to a manufacturing method of a liquidcrystal panel of the invention, using the microlens substrate, a liquidcrystal panel having long-term reliability and display accuracy can beobtained.

[0096] The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

What is claimed is:
 1. A method for manufacturing a microlens substratecomprising the steps of: forming a lens-shaped curve at a surface sideof a transparent substrate; forming an inorganic material film on saidtransparent substrate so as to bury said curve therewith; andplanarizing the surface of said inorganic material film to provide amicrolens where said curve is buried with said inorganic material film.2. The method according to claim 1, wherein the step of forming alens-shaped curve at a surface side of a transparent substratecomprises: forming a resist film on said transparent substrate; formingthe lens-shaped curve at a surface side of said resist film; andtransferring said lens shape from said resist film to the surface sideof said transparent substrate by dry etching.
 3. The method according toclaim 1, wherein the step of forming a lens-shaped curve at a surfaceside of a transparent substrate comprises: forming a mask pattern onsaid transparent substrate; and forming said lens-shaped curve at thesurface side of said transparent substrate by isotropic etching fromsaid mask pattern.
 4. The method according to claim 1, wherein saidinorganic material film is formed of at least one member selected fromthe group consisting of Al₂O₃, HfO₂, Ta₂O₅, Nb₂O₅ and ZrO₂.
 5. Themethod according to claim 1, wherein after the step of planarizing thesurface of said inorganic material film to provide a microlens wheresaid curve is buried with said inorganic material film, a cover filmhaving a given thickness is formed on said inorganic material film. 6.The method according to claim 1, wherein after the step of planarizingthe surface of said inorganic material film to provide a microlens wheresaid curve is buried with said inorganic material film, a thin filmtransistor is formed on said inorganic material film at a positioncorresponding to a peripheral portion of said microlens.
 7. The methodaccording to claim 6, wherein after the step of planarizing the surfaceof said inorganic material film to provide a microlens where said curveis buried with said inorganic material film, but prior to the formationof said thin film transistor, a light-shielding pattern is provided onsaid inorganic material film at the position corresponding to aperipheral portion of said microlens.
 8. A method for manufacturing aliquid crystal panel, which comprising the steps of: providing amicrolens substrate made by forming a lens-shaped curve at a surfaceside of a transparent substrate, forming an inorganic material film onsaid transparent substrate so as to bury said curve therewith,planarizing a surface of said inorganic material film to form amicrolens wherein said curve is buried with said inorganic materialfilm, and forming a thin film transistor on said inorganic material filmat a position corresponding to a peripheral portion of said microlens;placing a counter substrate in face-to-face relation with said microlenssubstrate at a thin film transistor-formed side thereof; and sealedlyfilling a liquid crystal layer between said microlens substrate and saidcounter substrate.
 9. A method for manufacturing a liquid crystal panel,which comprising the steps of: providing a first microlens substrate anda second microlens substrate, each made by forming a lens-shaped curveat a surface side of a transparent substrate, forming an inorganicmaterial film on said transparent substrate so as to bury said curvetherewith, and planarizing a surface of said inorganic material film toform a microlens wherein said curve is buried with said inorganicmaterial film; forming a thin film transistor on said inorganic materialfilm of said first microlens substrate at a position corresponding to aperipheral portion of the microlens; placing said first microlenssubstrate and said second microlens substrate in such a way that theplanarized surface of said first microlens substrate and a thin filmtransistor-formed side of said second microlens substrate are inface-to-face relation with each other keeping principal points of thetwo microlens substrates at a given distance; and sealedly filling aliquid crystal layer between said first microlens substrate and saidsecond microlens substrate.